I was trying to figure this out at one point. We know that prince and bard are male, and I believe we know that it's a six-six split between gendered and non. There are some that we know are non-gendered:

Knight: Dave and Latula

Seer: Rose and Kankri

Mage: Sollux and Meulin

Rogue: Roxy and Rufioh

For others we only see one gender, so some guesswork is required. Thief is probably non-gendered, it's a gender-neutral term and the counterpart of Rogue, which we know is non-gendered. The three female classes are likely Sylph, Witch, and Maid, with all three having feminine connotations. That gives us:

Knight: X

Seer: X

Mage: X

Rogue: X

Thief: X

Prince: M

Bard: M

Sylph: F

Witch: F

Maid: F

Heir: ?

Page: ?

This leaves either Heir or Page as the last male-exclusive class, and I'm really not sure which. I'd be inclined to say Page, as I think it has slightly more masculine connotations, but I'm not sure. Also, the whole thing is kind of dumb anyway! Degender the classes 2025.